Micronemadus sondaicus Schilthuizen & Perreau

Schilthuizen, Menno, Perreau, Michel & Njunjic, Iva, 2018, A review of the Cholevinae from the island of Borneo (Coleoptera, Leiodidae), ZooKeys 777, pp. 57-108 : 59-60

Micronemadus sondaicus Schilthuizen & Perreau sp. n. Figure 1a, c–f

Material.

Holotype: Malaysia, Sabah, Crocker Range Park, Inobong, 5°51.265'N, 116°08.363'E, 500 m elev., 21-23.ix.2012 (leg. M. Schilthuizen, Crocker Range / Kinabalu Expedition, RMNH.INS.555641), male. Paratypes: Sabah. Crocker Range Park, Inobong, 5°51.3'N, 116°08.4'E, 500 m elev., 21-23.ix.2012 (leg. M. Schilthuizen, Crocker Range / Kinabalu Expedition, RMNH.INS.555640, 555642), 2 individuals; Crocker Range, Gunung Alab, xii.2009 (leg. M. Schilthuizen, RMNH.INS.63291, 63310, 63295), 3 individuals; Crocker Range, along the road from Kota Kinabalu to Tambunan, near Rafflesia Park, 5°46.4'N, 116°20.8'E, 1350 m elev., baited pitfall trap, 2001 (leg. M. Schilthuizen, RMNH.INS.549293-549295), 3 individuals; Kinabalu Park, Headquarters Area, Liwagu Trail, 6°0.487'N, 116°32.7'E, pitfall with chicken, 2.iv.2016 (leg. M. Schilthuizen, I. Njunjić & F. Feijen, BORN, RMNH.INS.1086143-1086158), 36 individuals. Kinabalu Park, Sayap, ix.2012 (leg. M. Schilthuizen, Crocker Range / Kinabalu Expedition, BOR/COL/14178-14193), 16 individuals. Sarawak. Gunung Mulu National Park, many localities between 100 and 950 m elev., iii–viii.1978 (leg. P. M. Hammond & J. E. Marshall, NHMUK BM 1978-49), 131 specimens.

Description.

Length: 2.0-2.6 mm. Colouration: in fully coloured individuals dark brown to black, margins of pronotum and front half of the elytra reddish brown, entirely covered in reddish brown setae; legs, palps, and basal three and final antennomeres light reddish brown; antennomeres 4-10 darker (Figure 1a). Pronotum: small, much narrower than the elytra, ca. 2 times as broad as wide, with the greatest width slightly frontal of the caudal angles; basal margin gently emarginated near the angle, and with an angular sinuosity in the centre, on either side of the scutellum. Elytra: rounded at the apex, 1.25 times as long as jointly wide (length measured from the caudal tip of the scutellum to the apex of the elytra). Winged. Male protarsi: slightly narrower than the protibia, segments 1-4 as long as wide. Aedeagus: median lobe pointed, nearly perfectly triangular, parameres slender, extending far beyond the tip of the median lobe (Figure 1c). Female sternite VIII caudally broadly rounded, rostrally tapering into a narrow tip.

Differential diagnosis.

Similar to M. pusillimus (Kraatz, 1877), described from Japan, but compared with Japanese specimens of M. pusillimus that we have seen, M. sondaicus is larger, more uniformly coloured (Figure 1a; Japanese M. pusillimus have a more strikingly dark pronotum), has a simple triangular shape of the median lobe of the aedeagus (in M. pusillimus , the apex is separately acuminate; see Figure 1b), and more slender parameres (Figure 1c). The female sternite VIII in M. pusillimus is more slender and rostrally not as narrowly tapered as in M. sondaicus . M. ruzickai Perreau, 2004 differs by the parameres that are even more massive than in M. pusillimus .

DNA-barcodes.

In the BOLD database, COI sequences are available for the holotype (RMNH.INS.555641) and two paratypes (RMNH.INS.555640, 555642) from Inobong (Crocker Range) and also for the paratypes RMNH.INS.549293-549295 from Gunung Alab (Crocker Range). See also under Remarks.

Habitat and distribution.

Very common and widespread, in primary and secondary forest, 0-1850 m elev. In addition to the type material, we have seen seemingly conspecific material from many other localities in Sundaland, (Sabah, Sarawak, Peninsular Malaysia, Mindanao, Java, Bali) and also from Vietnam. Nishikawa’s (1989) records of M. pusillimus from Peninsular Malaysia, Sabah, Sarawak, Java, and Bali (which we did not see) may also refer to M. sondaicus . This overview suggests that M. sondaicus is widespread in Southeast Asia (but see below under remarks).

Remarks.

For many years, we considered this Borneo Micronemadus , which is usually the commonest leiodid in baited traps, as identical to M. pusillimus . However, DNA-barcodes for Japanese individuals (BOLD BIN ABU9390) and Bornean individuals (BOLDBINsABU9391 and ACK0008) display a 17% sequence divergence, strongly suggesting that, despite the only slight morphological differences, these belong to separate, not closely related species. We suspect that M. pusillimus , previously considered a very widespread Asian species ( Szymczakowski 1964), may represent a complex of genetically strongly differentiated, but morphologically very similar taxa. In fact, among the DNA-barcoded specimens of M. sondaicus from Sabah’s Crocker Range, we already see a 2.7% sequence divergence between highland and lowland populations, which has led the BOLD algorithm to place them into separate BINs (BOLD:ABU9391 and ACK008, respectively). At the moment, however, we consider ABU9391 and ACK008 as conspecific.

Etymology.

The name refers to the Sunda region, of which Borneo forms part ( sondaicus (L.) = from Sunda). We used the spelling sondaicus , rather than sundaicus, to conform with other specific epithetons, such as Rhinoceros sondaicus Desmarest, 1822.